Geometric Optics deals with wave phenomena/behaviours that involves the behaviour of waves as they encounter different media. This includes reflection refraction and dispersion. This page covers the basic principles, as well as some familiar applications.
Apart from what is provided below, a useful interactive that explores a number of these can be found at the Ray Optics Simulator
Apart from what is provided below, a useful interactive that explores a number of these can be found at the Ray Optics Simulator
1. Refraction Explained
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Light bends as it enters a different medium. What are the principles behind the amount it bends? |
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- Suppose that light rays traveling through air reach quartz at an angle of 31°. The index of refraction of quartz is 1.54. At what angle do the light rays travel within the quartz? (19.5°)
- A light ray enters a substance from the air at an angle of 35°. The light is refracted inside the substance and travels at an angle of 26°. What is the index of refraction of the substance? (1.308)
- Diamond has an index of refraction of 2.42. If it is immersed in water, which has an index of 1.33, and light rays in the water enter the diamond at a 34° angle, what is the angle of refraction inside the diamond? (17.9°)
- The index of refraction of a substance is 1.83. What is the speed of light in that material? (1.64e8)
- A ray of light strikes a mirror at an angle of incidence of 24°. What is the angle of reflection? (24°)
- A ray of light passes from an unknown substance into the air. If the angle in the unknown substance is 39.0° and the angle in the air is 53.0°, what is the index of refraction of the unknown substance? (1.27)
- A ray of light has an angle of incidence of 25.0° upon the surface of a piece of quartz. What is the angle of refraction? (15.9)
- A beam of light passes from water into polyethylene, index of refraction = 1.50. If the angle in the water is 36.0°, what is the angle in the polyethylene? (30.92)
- Mi-ling makes some hydrogen sulfide, index of refraction = 1.000 644. If Mi-ling measures an angle of 85.000 000° in the hydrogen sulfide, what angle will Mi-ling measure in air if the index of refraction of air is 1.000 292 6? (85.236°)
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This animation from pHet is a great way to explore refraction. Play with it, but better still, use the settings to determine variables and then use the built in tools to confirm you calculations , especially Snells' Law
2. Total Internal Reflection Explained
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Total internal reflection is a unique property of refraction as the wave enters a substance of lower refractive index/ an in class demo using water
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Use. the pHET animation to illustrate total internal reflection by adjusting the refractive indices
3. Lenses and virtual images
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When you look through a lens, it distorts the image. It may magnify it, it may not. It may be inverted or not. This video explains the principles using the concept of light paths |
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4. Lenses and real image formation
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How can a lens project a real image on to a screen? Using light paths, this video explains how
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This interactive from Tom Walsh allows you to move your object and see where the image is formed. Use the blue disk to move the object. You can also change the curvature of the lens by adjusting the focus. This is the red spot
5. The physics of the eye
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Your eye uses the concept of real image formation to project an image on your retina and the adjusts the amount of refraction through a process called accomodation. This video explores this. |
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This interactive allows to manipulate an 'object' and place it correctly so the image forms on the retina
(Unfortunately the interactive that I used from pHET no longer works due to running in Flash.)
(Unfortunately the interactive that I used from pHET no longer works due to running in Flash.)
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6. The reason behind dispersion
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Dispersion is the spreading of waves. So it all colour variations travel at the speed of light, why do some colours bend more than others? |
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